The present invention relates to a cross joint (joint cross coupling, universal joint) used in a steel rolling mill or the like.
In, for example, a steel rolling mill, a cross joint is interposed between a roll and a drive shaft for driving to rotate the roll, a steel rolling processing of the steel material can be carried out by rotating to move the role in accordance with rotation of the shaft while the roll is allowed to move in an up and down direction relative to a steel material which is being rolled. The cross joint includes: a cross shaft member (cross) having four shafts arranged in a cross-like shape; and a cross bearing which has a plurality of cylindrical rollers as rolling members aligned at surroundings of the respective shafts of the member, and a bearing cup as an outer ring mounted to an outer side of outer peripheries of the rollers. Each of outer peripheral portions of the shafts is used as an inner ring race portion. Further, according to the cross joint, the roll and the drive shaft are connected to a first shaft and a second shaft comprising respective pairs of shafts arranged on straight lines in the four shafts respectively via the cross bearings and (rotational) torque from the shaft is transmitted to the roll via the cross joint.
Meanwhile, according to the above-described conventional cross joint, such a cross shaft member and the bearing cup are provided, which are generally constituted by bearing steel of carburized steel or the like.
However, when large torque acts on the cross joint such as in the steel rolling mill, the joint is used under a very severe condition and there is a concern that even when the bearing steel is used, malfunction is brought about at an early stage. In details, the cylindrical roller is rolled on the inner ring race portion or the like formed at the cross shaft member under high contact surface pressure and therefore, exfoliation is liable to be brought about at the race portion. Further, according to the cross member, since the roll and the drive shaft are respectively connected to the contiguous pairs of shafts and therefore, large bending stress may be operated to a shoulder portion between shaft root (shaft neck) portions thereof and fatigue breaking of bending fatigue breaking or the like is liable to be brought about at the member.